Annual ring validation of the South African sardine Sardinops sagax using daily growth increments

Abstract

A total of 21 sardine Sardinops sagax otoliths, collected in winter and spring 1994, were examined with a scanning electron microscope to validate growth zones using daily growth increments. Increment numbers and widths for the first, second and third annual growth zones served to back-calculate hatching dates and to validate the assumption that the identified annual rings were deposited in annual intervals. Fish appeared to have hatched throughout 1992. Annual ring deposition periods depended on the individual cases and did not correspond to exactly one year, with some fish estimated to be older than one year at the first annual ring deposition. The second growth zone contained a mean of 266 daily increments, with the second annual ring deposited between November 1993 and June 1994. The third annual ring was visible on six otoliths, and appeared to have been deposited in August and September 1994.